JP2011222360A - Light source driving device, image processing device, image reading device, and image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To speed up boosting without generating overvoltage.SOLUTION: The light source driving device comprises load means (a second load) 20 consuming power equal to that of a plurality of LED light sources (a first load) 10 and a connection switching circuit 50 which switches connection so as to selectively connect either one of the plurality of the LED light sources 10 or the second load 20 between a boosting circuit 30 and an LED driver 40. When the lighting-up of the first load 10 is started, the second load 20 is connected to the boosting circuit 30, and feeding voltage Vin from a power source is boosted by the boosting circuit 30. After the boosting is completed, the first load 10 is switched to connect to the boosting circuit 30.

Description

  The present invention relates to a light source driving apparatus that drives a plurality of light sources, an image processing apparatus including the light source driving apparatus, and an image reading apparatus (an image such as a scanner apparatus mounted on an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine) The present invention relates to a reading device or an image reading device such as a single scanner device, and an image forming apparatus equipped with the light source driving device or the image reading device.

  For example, there is a light source used in a scanner device in which a plurality of chip LEDs (Light Emitting Diodes) are arranged. When driving such a light source, since it is more efficient that more LEDs can be driven per driver chip, many LED driver ICs (hereinafter simply referred to as “LED drivers”) are supplied to the LEDs. It has a function to boost the voltage (feed voltage) to be used and has already been put into practical use. Since the LED is a semiconductor component, it has excellent luminous efficiency and responsiveness, and a large amount of light can be obtained with low power consumption. In addition, there is an advantage that the light quantity stabilization wait time before scanning is almost unnecessary.

  However, in such a conventional LED driver and its peripheral circuit configuration, no power is required except during the LED lighting state (the state in which the LED is operating as a load), and therefore the boosting operation cannot be performed. That is, the boosting operation is performed only while the LED is lit. Therefore, when performing lighting control (PWM lighting control) by pulse width modulation (PWM), for example, as shown in FIG. 11, the boosting operation is performed in a time-divided manner, and the steady state (boosting) The time required to reach the complete state) is required to be 1 / Duty (duty) or more as compared with the time of full lighting (always lighting), and it is necessary to set a long light quantity stabilization weight from LED lighting to scanning start. As a result, there has been a problem that the throughput (productivity) of image formation is reduced, such as the first copy time being delayed.

  Therefore, in order to solve the problem, it is conceivable to perform the boosting operation by fully lighting the LED for the purpose of speeding up the boosting. However, since the LED emits more light than necessary, the CCD (Charge Coupled Device) ) There is a concern that an image sensor (hereinafter simply referred to as “CCD”) receives an excessive amount of light, and the output characteristics of all circuit components including the CCD reach a saturated state. As a result, there are problems that it takes time to return each component to the active state, and there is a risk of destruction due to the occurrence of overvoltage. For this reason, many have a configuration in which the high-speed rise of the light amount of the LED cannot be fully utilized.

Therefore, in order to solve the problem, it is conceivable to use the technique disclosed in Patent Document 1.
In Patent Document 1, for the purpose of reducing power consumption and improving operational stability, when the battery voltage is higher than a predetermined voltage, a dummy load is connected in series with the load, and the battery voltage is equal to or lower than the predetermined voltage. Discloses a configuration in which a switching unit for short-circuiting the dummy load is provided.

However, since the device described in Patent Document 1 has a configuration in which the LED is lit, there is a concern that the component characteristics of the CCD and other read signal processing circuits may reach a saturation level or an overvoltage may occur. Has not been resolved.
The present invention has been made in view of the above points. In the light source driving device, the object is illuminated by light emitted from a light source such as a plurality of LEDs, and processing is performed by receiving reflected light from the object. An object of the present invention is to increase the speed of voltage boosting without generating an overvoltage with respect to circuit components (CCD, other read signal processing circuit, etc.) provided in each apparatus such as an image processing apparatus to be performed.

  In order to achieve the above object, the present invention provides a light source driving device, an image processing device, an image reading device, and an image forming device shown in the following (1) to (12).

(1) A light source driving apparatus for driving a plurality of light sources, the step-up means for boosting a power supply voltage from a power source to supply the plurality of light sources, and the plurality of light sources to which the boosted voltage is applied Constant current drive means for making the drive current constant constantly, load means for consuming the same power as the plurality of light sources, and selectively boosting one of the plurality of light sources and the load means And a connection switching means for switching the connection so as to be connected to the constant current driving means.

(2) In the light source driving device of (1), the connection switching means connects the load means to the boosting means until the boosting is completed after the boosting starts by the boosting means, and after the boosting by the boosting means is completed. The connection is switched so that the plurality of light sources are connected to the boosting means.
(3) In the light source driving device of (2), the connection switching means switches the connection in synchronization with an external control signal.

(4) In the light source driving device of (2), the constant current driving unit is a unit that is activated by an activation signal from the outside, and the connection switching unit is configured to perform connection switching based on the activation signal. Signal generation means for generating a signal is provided.
(5) In the light source driving device according to any one of (1) to (4), when the plurality of light sources are driven by the constant current driving unit, the plurality of light sources are electrically cut off so that the driving currents do not wrap around each other. A blocking means is provided.

(6) In the light source driving device of (5), a diode is used as the blocking means.
(7) In the light source driving device according to any one of (1) to (6), a resistor is used as the load means.
(8) In the light source driving device according to any one of (1) to (7), the light source driving device is configured by one integrated circuit.

(9) The light source driving device according to any one of (1) to (8) is provided, the subject is illuminated with light emitted from the plurality of light sources by the light source driving device, reflected light from the subject is received, and an image is received. An image processing apparatus that performs image processing by converting a signal.
(10) The image processing apparatus of (9) is an image reading apparatus, and reads the image data of the subject by the image processing.

(11) An image forming apparatus including the image reading apparatus according to (10) and an image forming unit that forms an image on a recording medium based on image data read by the image reading apparatus.
(12) The light source driving device according to any one of (1) to (8), and an image carrier that is precharged by the reflected light from the subject by illuminating the subject with the irradiation light from the plurality of light sources thereby An image forming apparatus includes an image forming unit that exposes the image to form an image.

  According to this invention, the light source driving device selectively selects one of the load means (second load) that consumes the same power as the plurality of light sources (first load), and the plurality of light sources and the load means. Connection switching means for switching the connection so as to be connected between the boosting means and the constant current driving means, and when starting lighting of a plurality of light sources, the load means is connected to the boosting means from the power source. Since the power supply voltage from the power source is constantly boosted by switching the connection so that the plurality of light sources are connected to the voltage boosting means after the power supply voltage is boosted by the voltage boosting means, the irradiation light from the plurality of light sources is Without causing overvoltage to circuit components included in each apparatus such as an image processing apparatus, an image reading apparatus, and an image forming apparatus that perform processing by illuminating the object by receiving reflected light from the object. Boosting the speed can be increased.

It is a circuit diagram which shows an example of the basic composition of the light source drive device which is 1st Embodiment of this invention. It is a flowchart which shows the operation example of the timing clock generation part in the scanner apparatus provided with this light source drive device shown in FIG. It is a circuit diagram which shows the 1st example of a specific structure of the light source drive device which is 2nd Embodiment of this invention. It is a flowchart which shows the operation example of the timing clock generation part in the scanner apparatus provided with the light source drive device shown in FIG. It is a circuit diagram which shows the 2nd example of the specific structure of the light source drive device which is 3rd Embodiment of this invention.

FIG. 6 is a timing chart showing operation timings according to input / output signals of the light source driving device shown in FIG. 5. It is a circuit diagram which shows the 3rd example of a specific structure of the light source drive device which is 4th Embodiment of this invention. It is a whole block diagram which shows the structural example of the mechanism part of the image reading apparatus which is 5th Embodiment of this invention. FIG. 9 is a block diagram illustrating a configuration example of a part of an image signal processing unit of the image reading apparatus 100 illustrated in FIG. 8. It is a whole block diagram which shows the structural example of the mechanism part of the image forming apparatus which is 6th Embodiment of this invention. It is a figure for demonstrating the operation | movement immediately after LED lighting by the conventional LED driver and its peripheral circuit structure.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings. In this embodiment, an LED (hereinafter also referred to as “LED light source”) is used as the light source, but other light sources may be used.
In the following embodiments, the light source driving device has the following characteristics in the step-up operation at the start of LED driving.

That is, a load unit (second load) that consumes (has a load) equivalent to the power of the plurality of LEDs (first load), and selectively selects one of the plurality of LEDs and the load unit and the constant current. And a connection switching means for switching the connection so as to be connected to the driving means, and when starting lighting of the plurality of LEDs, the load means is connected to the boosting means and the power supply voltage from the power source is boosted by the boosting means. After that, the power supply voltage from the power source is constantly boosted by switching the connection so that the plurality of LEDs are connected to the boosting means.
Therefore, the feature will be described in detail.

[First Embodiment]
First, a first embodiment of the present invention will be specifically described with reference to FIGS.
FIG. 1 is a circuit diagram showing an example of a basic configuration of a light source driving apparatus according to the first embodiment of the present invention.
The light source driving device includes a first load 10, a second load 20, a booster circuit 30, an LED driver 40, and a connection switching circuit 50.

The first load 10 is a plurality of LEDs (light sources).
The second load 20 is a load means such as a resistor that consumes power equivalent to that of the first load 10.
The booster circuit 30 is a booster that boosts the power supply voltage (reference voltage) Vin from the power supply and supplies the boosted voltage to the first load (a plurality of LEDs) 10.
The LED driver 40 is a constant current driving unit that includes a constant current source (constant current circuit) and that constantly drives the driving current of the first load 10 to which the voltage boosted by the boosting circuit 30 is applied.

  The connection switching circuit (SW) 50 is connection switching means for switching the connection so as to selectively connect either the first load 10 or the second load 20 between the booster circuit 30 and the LED driver 40. . The connection switching circuit 50 connects the second load 20 to the booster circuit 30 from the start of boosting by the booster circuit 30 to the completion of boosting, and after the boosting by the booster circuit 30 is completed, the first load (a plurality of LEDs). The connection is switched so that 10 is connected to the booster circuit 30.

FIG. 2 is a flowchart showing an operation example of a timing clock generation unit (not shown) in the scanner apparatus provided with the light source driving apparatus shown in FIG. The configuration of the scanner device will be described in detail later.
The timing clock generation unit of the scanner device waits for input of an LED drive start signal from a CPU (not shown) in step S1 of FIG. 2 when the first load (a plurality of LEDs) 10 is turned off.

When the LED drive start signal is input, the process proceeds to step S2.
In step S2, an activation signal is input to the LED driver 40 to activate the LED driver 40, and the load switching control signal (switching signal) is set to the high level “H”, whereby the power load is changed to the second load 20. Drive as.

  When the switching signal from the timing clock generator becomes “H”, the connection switching circuit 50 switches the connection so that the second load 20 is connected to the booster circuit 30 in order to boost the power supply voltage from the power supply. Thereby, the LED driver 40 activates the internal constant current source and the booster circuit 30 to start the LED lighting operation. Thereby, the booster circuit 30 starts boosting the power supply voltage from the power supply (power boost).

Here, boosting of the supply voltage from the power supply is performed in order to drive more LEDs with the LED driver (driver 1 chip).
Further, conventionally, immediately after the start of the LED lighting operation, the LED is in an extinguished state and is not operating as a use load (not consuming electric power), so the boosting is stopped. For this reason, in the case of repeatedly driving and stopping when the LED is turned on by the PWM drive control signal, the step-up operation at the start of turning on the LED is also divided. Therefore, there is a concern that the time until the completion of boosting is extended.

Therefore, in this embodiment, until the boosting is completed, the second load 20 which is a load different from the first load (a plurality of LEDs) 10 is used for boosting, and the first load (a plurality of LEDs) 10 is changed. Boosting is completed without lighting. Thereby, the wait (waiting time) until the first load is turned on can be shortened.
Returning to FIG. 2, the timing clock generation unit waits for the elapse of a predetermined time set in advance after starting the LED lighting operation in step S <b> 3.

When the specified time elapses, that is, when the boosting is completed, the process proceeds to step S4, where the switching signal is set to the low level “L”, thereby setting the power source load as the first load (a plurality of LEDs) 10 and the light source driving device. Drive.
Thereafter, when a document scan, which will be described later, is completed, the process proceeds to step S5, and the input of the activation signal to the LED driver 40 is stopped to turn off the first load 10 in an OFF state.

  The connection switching circuit 50 is connected so as to connect the first load (a plurality of LEDs) 10 to the booster circuit 30 in order to perform a normal LED lighting operation when the switching signal from the timing clock generator becomes “L”. Switch. Therefore, the scanner device provided with the light source driving device can scan the original and read the image data.

That is, immediately after the start of the LED lighting operation, the power supply voltage from the power source is boosted using the second load 20, and after the lapse of the specified time (after reaching the LED driveable voltage), the first load (a plurality of loads) LED) 10 is driven as a use load (PWM drive).
Note that the above connection switching timing determination is used as a voltage, and connection switching is also possible by determining whether the boosted voltage has reached a preset specified potential. However, since the circuit configuration is complicated, the time specification is More realistic. That is, since the specified time corresponds to the light quantity stabilization weight before the start of scanning, the conventional software function can be used as it is.

  According to the light source driving device of the first embodiment, a load unit (second load) that consumes the same power as a plurality of LED light sources (first load), and one of the plurality of LED light sources and the load unit is selected. And a connection switching circuit for switching the connection so as to be connected between the booster circuit and the LED driver, and when starting lighting of the plurality of LED light sources, the load means is connected to the booster circuit to supply power from the power source. After the voltage is boosted by the booster circuit and the boosting is completed, the connection voltage is switched so that the plurality of LED light sources are connected to the booster circuit, thereby constantly boosting the power supply voltage from the power source.

In addition, since the constant current source of the first load (LED light source) and the second load is shared, the step-up rate difference (component characteristic error) between the first load and the second load is minimized, Since voltage readjustment after completion of boosting and switching of the load is almost unnecessary, the boosting speed is increased.
Further, since each LED light source is not turned on at the start of voltage boosting, an image processing device, an image reading device, and an image processing are performed by illuminating a subject with light emitted from each LED light source and receiving reflected light from the subject. It is possible to prevent the occurrence of overvoltage with respect to each circuit component (CCD or other read signal processing circuit) included in each apparatus such as a forming apparatus, and to avoid the fear of destruction of each circuit component.

[Second Embodiment]
Next, a second embodiment of the present invention will be specifically described with reference to FIGS.
FIG. 3 is a circuit diagram showing a first example of a specific configuration of the light source driving apparatus according to the second embodiment of the present invention, and portions corresponding to those in FIG.
The light source driving device according to the second embodiment is an application example of the light source driving device according to the first embodiment, and the first load 10 includes a plurality of LED light source rows 10a, 10b,. . In addition, the switching of the connection as described above is performed by a switching signal Control. Signal. (Hereinafter abbreviated as “cont.sig.”).

Switching signal cont. sig. Becomes “H” only for a specified time from the start of driving of the LED driver 40 until the boosting of the power supply voltage from the power supply is completed, and thereafter maintains “L”.
Further, the PWM drive control signal input to the input terminal PWM of the LED driver 40 is converted into a PWM clock signal PWM_CLK and a switching signal cont. sig. Are ORed (logically ORed) so that the constant current drive with the second load (resistor) 20 is completed until the boosting is completed, and the first load 10 (LED light source arrays 10a, 10b,. ., 10n) PWM drive. The prescribed time can be set to be variable by an operation signal from an external device.

  The LED driver 40 monitors the terminal voltages of the channel terminals (output terminals) ch_1, ch_2,..., Ch_N when adjusting the boosted voltage level. Therefore, when the second load 20 is driven by the LED driver 40, the same configuration as when the first load 10 is driven (the load is connected to each channel terminal) eliminates the need for switching the operation when switching the connection (load). In addition, load fluctuation can be minimized.

  The diode circuit Da, Db,..., Dn is a cutoff circuit 70 for preventing the influence of the second load 20 when the LED driver 40 drives the first load 10, that is, the LED light source arrays 10a, 10b. ,..., 10n are blocking means for electrically blocking the drive currents so as not to sneak into each other. When this is not arranged, the channel terminals ch_1, ch_2,..., Ch_N of the LED driver 40 are connected through a short state or a load when the first load 10 is driven, and the LED light source arrays 10a, 10b,. .., 10n has different current behavior from each of the channel terminals ch_1, ch_2, ..., ch_N of the LED driver 40.

FIG. 4 is a flowchart showing an operation example of a timing clock generation unit (not shown) in the scanner apparatus provided with the light source driving apparatus shown in FIG.
The timing clock generator of the scanner device waits for the input of the LED drive start signal in step S11 of FIG. 4, and proceeds to step S12.
In step S12, the enable signal EN (ON / OFF), which is an activation signal input to the LED driver 40, is set to the high level “H” to activate the LED driver 40, and the switching signal cont. sig. Is set to “H” to drive the power load as the second load 20.

  The connection switching circuit 50 includes a switching signal cont. Input to the enable terminal EN2 from the timing clock generator. sig. Becomes “H”, the connection between the input terminal I2 and the output terminal O2 becomes conductive (ON), and the connection is switched so that the second load 20 is connected to the booster circuit 30. Thereby, the LED driver 40 activates the internal constant current source and the booster circuit 30 to start the LED lighting operation. Thereby, the booster circuit 30 starts boosting the power supply voltage from the power source.

Next, the timing clock generator waits for the elapse of the specified time set in step S13 (the boosting is completed), and then proceeds to step S14, where the switching signal cont. sig. To “L”, the light source driving device is driven with the power load as the first load 10.
Thereafter, when the document scanning is completed, the process proceeds to step S15, and the enable signal EN (ON / OFF) to be input to the LED driver 40 is set to “L” in order to turn off the first load 10.

  The connection switching circuit 50 includes a switching signal cont. Input from the timing clock generator to the enable terminal EN1. sig. Becomes “H”, the connection between the input terminal I 1 and the output terminal O 1 becomes conductive (ON), and the connection is switched so that the first load 10 is connected to the booster circuit 30. Therefore, the scanner device provided with the light source driving device can scan the original and read the image data.

According to the light source driving device of the second embodiment, the following effects (a) to (d) can be obtained in addition to the same effects as the first embodiment.
(A) Since the connection switching circuit performs load connection switching in synchronization with a switching signal that is a control signal for load switching from the outside, the switching can be performed at an arbitrary and highly accurate timing.

(B) When the plurality of LED light source arrays (first load) are driven by the LED driver, the interrupt circuit is electrically disconnected so that the drive currents do not wrap around each other, so that each LED driver array It is also possible to prevent a difference between the current behavior of the channel terminal and the current behavior of each LED light source array.
(C) By using a resistor for the second load, the configuration of the second load can be facilitated and the cost can be reduced. (D) By using a diode, which is a general-purpose component, in the cutoff circuit, the cutoff can be achieved. The circuit configuration can be simplified, the cost can be reduced, and high reliability can be realized.

[Third Embodiment]
Next, a third embodiment of the present invention will be specifically described with reference to FIGS.
FIG. 5 is a circuit diagram showing a second example of the specific configuration of the light source driving apparatus according to the third embodiment of the present invention. The same reference numerals are given to the same portions as those in FIG.
In the light source driving device of the third embodiment, the switching signal cont. sig. Instead, an RC circuit 80 (which may be another circuit) which is a signal generation means is added, and an enable signal EN (ON / OFF) from the outside (timing clock generation unit) is supplied to the RC circuit 80 during RC. Delayed by a constant, the switching signal cont. sig. Have the same function.

FIG. 6 is a timing chart showing operation timings according to input / output signals of the light source driving device shown in FIG.
(1) Initially, since the enable signal EN (ON / OFF) is “L”, both the LED driver (DRV) 40 and the first load 10 (LED light source arrays 10a, 10b,..., 10n) are off. State. Since the enable signal EN = “L”, the transistor Tr1 in the RC circuit 80 is in an on state, and the input terminal PWM of the LED driver 40 has a high level that is a power supply voltage (power supply voltage level) from the power supply. A signal is input and does not depend on the signal level of the PWM clock signal PWM_CLK.

(2) When the enable signal EN (ON / OFF) becomes “H”, the LED driver 40 starts a constant current operation and a boost operation (actually, a boost operation by the boost circuit 30). Here, the terminal voltages of the enable terminals EN1 and EN2 of the connection switching circuit 50 and the voltage Vbe between the base terminal b and the emitter terminal e of the transistor Tr1 are delayed by the resistors R1, capacitor C1, resistor R2, and capacitor C2, respectively. In the connection switching, a delay corresponding to a time constant is generated from the enable signal EN = “H”.

  On the other hand, in the LED driver 40, the signal (enable signal EN) to its enable terminal EN is “H” and the signal to the input terminal PWM (PWM clock signal PWM_CLK) is also “H”, and the connection switching circuit ( Since the signal to the enable terminal EN2 of (SW) 50 is “H”, driving is started with the power load being the second load 20. This operation is continued until the charge levels of the capacitors C1 and C2 reach the threshold value of each terminal voltage. The resistor R1, capacitor C1, resistor R2, and capacitor C2 are set to appropriate constants in consideration of the time until charging is completed, so that connection switching in the connection switching circuit 50 upon completion of boosting is automatically performed.

(3) When the charge levels of the capacitors C1 and C2 reach a predetermined threshold value, the transistor Tr1 = OFF → the signal to the input terminal PWM (PWM drive control signal) = PWM clock signal PWM_CLK, with the enable terminal EN = “H”. Since the signal to the enable terminal EN1 of the connection switching circuit (SW) 50 becomes “H”, the power load becomes the first load 10, and the first load 10 is driven according to the PWM clock signal PWM_CLK.

  According to the light source driving device of the third embodiment, the same operational effects as the first embodiment and the same operational effects as the above (b) to (d) of the second embodiment can be obtained. In addition, the RC circuit generates a signal for causing the connection switching circuit to perform connection switching based on an external activation signal for activating the LED driver, thereby facilitating the configuration by reducing the signal lines. Can be realized. Further, by changing the time constant of the RC circuit, the load connection can be switched at an arbitrary and highly accurate timing.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be specifically described with reference to FIG.
FIG. 7 is a circuit diagram showing a third example of the specific configuration of the light source driving apparatus according to the fourth embodiment of the present invention. The same reference numerals are given to the same parts as those in FIG.
In this light source driving device, an LED driver 90 constituting a single integrated circuit includes a driver 40 'having a function equivalent to that of the LED driver 40 shown in FIG. 5, a connection switching circuit 50, a cutoff circuit 70, and an RC circuit. 80 and the first load 10 and the second load 20 are externally attached to reduce costs and save space. Since the main load (resistance in this example) Z of the second load 20 can be externally attached, the load (electric power) of the second load 20 depends on the load and number of LEDs constituting the first load 10 to be driven. Consumption) is adjustable. Each circuit such as the LED driver 40 shown in FIG. 3 can also be incorporated.

  According to the light source driving device of the fourth embodiment, the same effects as those of the second or third embodiment can be obtained. Further, by configuring a part of the light source driving device with one integrated circuit, it is possible to realize cost reduction and space saving by incorporating functions in the integrated circuit.

  In the first to fourth embodiments described above, the second load that consumes the same power as the LED light source (first load) is provided in parallel, thereby providing a mechanism that can increase the boosting speed. Because it does not light up, it has the feature that there is no concern in terms of hardware. In the following fifth and sixth embodiments, examples in which the characteristics are applied to an image reading apparatus and an image forming apparatus which are image processing apparatuses will be described. The image processing device illuminates an image surface of a document that is a subject with irradiation light from a plurality of LED light sources by a light source driving device, and reflects light from the image surface with a CCD (or other image sensor). It receives light, converts it into an image signal, and performs image processing.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be specifically described with reference to FIGS.
FIG. 8 is an overall configuration diagram showing a configuration example of a mechanism unit of an image reading apparatus according to the fifth embodiment of the present invention.

  This image reading device is a scanner device or a single scanner device mounted on an image forming apparatus such as a digital copying machine, a digital multifunction peripheral, or a facsimile machine, and has a light source driving unit (FIG. 1, FIG. 3, FIG. 5, or FIG. 7) and an image signal processing unit, and illuminates a document as a subject with light emitted from the light source unit (first load 10) by the light source driving unit, and reflects light from the document. Can be received by a CCD, converted into an image signal by an A / D converter, subjected to image processing, and image data of a document can be read. Since the image signal converted by the A / D converter is an analog signal, it is converted to a digital signal.

  As shown in FIG. 8, the image reading apparatus 100 includes a contact glass 101 on which a document is placed, a first carriage 106 including a light source 102 for document exposure and a first reflection mirror 103, a second reflection mirror 104, and Various distortions caused by the second carriage 107 including the third reflecting mirror 105, a CCD linear image sensor (hereinafter simply referred to as “CCD”) 109, a lens unit 108 for forming an image on the CCD 109, and a reading optical system are corrected. A white reference plate 110 and a sheet-through reading slit 111 are provided.

An automatic document feeder (hereinafter abbreviated as “ADF”) 120 that is an automatic document feeder is mounted on the upper part of the image reading apparatus 100, and the ADF 120 is opened and closed with respect to the contact glass 101. It is connected via a hinge or the like (not shown) so that it can be made.
The ADF 120 includes a document tray 121 as a document placement table on which a document bundle composed of a plurality of documents can be placed, and a sheet through reading slit that separates the documents one by one from the document bundle placed on the document tray 121. And a separation / feeding unit including a feeding roller 122 that automatically feeds the toner to 111.

In the image reading apparatus 100 configured as described above, the following reading operation is performed in the scan mode in which the image surface of the document is scanned (scanned) to read the image of the document.
That is, the first carriage 106 and the second carriage 107 are moved in the arrow A direction (sub-scanning direction) at different speeds so that the optical path length is not changed by a stepping motor (not shown).

  At the same time, the image surface, which is the lower surface of the document set on the contact glass 101, is illuminated by the light source 102 of the first carriage 106 (corresponding to the first load 10 shown in FIGS. 1, 3, 5, and 7). (Exposure). Then, the reflected light image from the image surface is sequentially sent to the CCD 109 via the first reflecting mirror 103 of the first carriage 106, the second reflecting mirror 104 and the third reflecting mirror 105 of the second carriage 107, and the lens unit 108. The image of the original is read.

On the other hand, in the sheet-through mode in which an original is automatically fed and an original image is read, the following reading operation is performed.
That is, after the first carriage 106 and the second carriage 107 move to the lower side of the sheet through reading slit 111, the document placed on the document tray 121 is moved by the feed roller 122 in the direction indicated by the arrow B (sub-scanning direction). ) Is automatically fed.

  Since the lower surface (image surface) of the automatically fed document is illuminated by the light source 102 of the first carriage 106 at the position of the sheet-through reading slit 111, the reflected light image from the image surface is the first carriage. The image is sequentially sent to the CCD 109 via the first reflection mirror 103, the second reflection mirror 104 and the third reflection mirror 105 of the second carriage 107, and the lens unit 108, and an image of the original is read. The document whose reading has been completed is discharged to a discharge port (not shown).

Note that the image of the white reference plate 110 is read by illumination by the light source 102 started before the image reading in the scan mode or the sheet through mode, and shading correction at the time of image reading is performed based on the reading result. Since this shading correction is a known technique, a detailed description thereof will be omitted.
Further, when the ADF 120 is provided with a conveyance belt, the document can be automatically fed to the reading position on the contact glass 101 by the ADF 120 and the image of the document can be read even in the scan mode.

FIG. 9 is a block diagram illustrating a configuration example of a part of the image signal processing unit of the image reading apparatus 100 illustrated in FIG. 8.
In the image signal processing unit 150, the analog image signal photoelectrically converted by the CCD 109 is output to the analog processing circuit unit 151 as shown in FIG.
The analog processing circuit unit 151 performs various image processing such as sample hold processing and black level correction on the analog image signal input from the CCD 109, and then outputs the analog image signal to the A / D conversion circuit unit 152.

The A / D conversion circuit unit 152 converts the analog image signal input from the analog processing circuit unit 151 into a digital image signal (image data), and outputs the digital image signal to the subsequent image signal processing unit via the LVDS interface 153.
The timing clock generator 154 receives various timing clock signals to be input to the CCD 109, the analog processing circuit 151, the A / D conversion circuit 152, the LVDS interface 153, and the stepping motor (not shown) and the light source driving device in the image reading apparatus 100. It is generated and supplied based on a reference clock from the oscillator 155.

Of the timing clock signals generated by the timing clock generator 154, the signal input to the light source driver is an activation signal or switching signal input to each of the light source drivers of the first to fourth embodiments. It is each signal such as. Note that these signals can also be generated by a control unit using a CPU (Central Processing Unit) (not shown).
The light source driving unit generates a light source driving signal (driving current) synchronized with the reading line and the signal based on the signal from the timing clock generation circuit unit 154 and outputs the light source driving signal to the corresponding LED light source. The adverse effect on the image can be minimized.

  According to the image reading apparatus of the fifth embodiment, the light source driving apparatus according to any one of the first to fourth embodiments is provided, and the original is illuminated with light emitted from a plurality of LED light sources by the light source driving apparatus. By receiving the reflected light from the light and converting it into an image signal to perform image processing, reading the image data of the original avoids a decrease in productivity (image reading throughput) such as slow image reading. be able to. In addition, it is possible to avoid concern about destruction of circuit components due to the occurrence of overvoltage. Therefore, it is possible to realize high image quality of the read image, high speed image reading, and high processing efficiency.

[Sixth Embodiment]
Next, a sixth embodiment of the present invention will be specifically described with reference to FIG.
FIG. 10 is an overall configuration diagram showing a configuration example of a mechanism portion of an image forming apparatus according to the sixth embodiment of the present invention. The same reference numerals are given to the same portions as those in FIG.
The image forming apparatus 200 is a digital copier equipped with the image reading apparatus 100 shown in FIG. 8 (including a light source driving unit corresponding to the light source driving apparatus shown in FIG. 1, FIG. 3, FIG. 5, or FIG. 7). Thus, the image data of the document can be read in the same manner as the image reading apparatus.

As shown in FIG. 10, the image forming apparatus 200 is provided with an ADF 300 on an upper part of a contact glass 101 on which an original is placed. A hinge or the like (not shown) is provided so that the ADF 300 can be opened and closed with respect to the contact glass 101. It is connected through.
The ADF 300 is placed on the document tray 301 with the image surface facing upward by pressing a print key on a document tray 301 as a document placement table on which a bundle of documents composed of a plurality of documents can be placed, and an operation unit (not shown). A separating roller / feeding means including a feeding roller 302 and a conveying belt 303 for separating and feeding the originals one by one from the bundle of originals and feeding them to the sheet-through reading slit 111 or the contact glass 101. ing.

The document fed by the feeding roller 302 or the conveyance belt 303 is read out as described with reference to FIG. 8 and then discharged onto the upper surface of the ADF 300 by the conveyance belt 303 and the discharge roller 304.
Here, the operation of the controller (not shown) and the ADF 300 when the document is conveyed to the reading position of the contact glass 101 by the ADF 300 will be described.

  The feed motor of the ADF 300 is driven by an output signal from the controller. When the feed start signal generated by pressing the print key on the operation unit is input, the controller corrects the feed motor.・ Reverse drive. When the feeding motor is driven to rotate in the forward direction, the feeding roller 302 rotates clockwise to automatically feed the document located at the uppermost position from the document bundle toward the sheet through reading slit 111 or the contact glass 101. Be transported. When the leading edge of the document is detected by the document set detection sensor 305, the controller drives the feed motor in the reverse direction based on the output signal from the document set detection sensor 305. This prevents subsequent documents from entering and prevents separation.

  When the document set detection sensor 305 detects the trailing edge of the document, the controller also counts a rotation pulse of a conveyance belt motor (not shown) from this detection point, and when the rotation pulse reaches a predetermined value, the conveyance belt 303 Is stopped and the conveying belt 303 is stopped, whereby the document is stopped at the reading position on the contact glass 101. Further, when the trailing edge of the document is detected by the document set detection sensor 305, the feeding motor is driven again so that the subsequent document is separated and automatically fed as described above and directed toward the contact glass 101. When the pulse of the feed motor from the time when the document is detected by the document set detection sensor 305 reaches a predetermined pulse, the feed motor is stopped to wait for the next document in advance.

  When the document stops at the reading position on the contact glass 101, the image of the document is read. When this image reading is completed, a signal indicating that is input to the controller, so that the controller drives the conveyance belt motor in the normal direction by this signal, and the document is discharged from the contact glass 101 by the conveyance belt 303 to the discharge roller. Unload to 304.

In this way, the document bundle placed on the document tray 301 in the ADF 300 with the image surface of the document facing up is automatically fed from the top document by pressing the print key. For example, the reading position on the contact glass 101 It is conveyed to.
The document that has been transported to the reading position and stopped is discharged from the discharge port by the transport belt 303 or the like after the image is read. Further, when it is detected that there is a next document on the document tray 301, the next document is automatically fed and conveyed onto the contact glass 101 in the same manner as the previous document.

  The transfer sheets (paper sheets) stacked on the first tray 201, the second tray 202, and the third tray 203, which are paper feed trays, are a first paper feed unit 211, a second paper feed unit 212, and a third paper feed unit, respectively. The sheet is fed by 213 and conveyed by the vertical conveyance unit 214 to a position where it abuts on a drum-shaped photosensitive member (photosensitive drum) 215 as an image carrier. Actually, any one of the trays 201 to 203 is selected, and the transfer paper is fed therefrom. Also, a recording medium other than transfer paper can be used.

On the other hand, the image data read by the image reading apparatus 100 is written on the surface of the photosensitive member 215 that has been charged in advance by a charging unit (not shown) by a laser beam from a writing unit 250 in the printer, which is an image forming unit. When the surface is exposed), the portion passes through the developing unit 227, and a toner image is formed there. The developing unit 227 and the charging unit that perform the image formation constitute an image forming unit.
The transfer paper fed from the selected paper feed tray is transferred by the transfer belt 216 at the same speed as the rotation of the photoconductor 215, and the toner image on the photoconductor 215 is transferred. Further, the toner image is fixed by the fixing unit 217, and is discharged by a paper discharge unit 218 to a paper discharge tray 219 outside the apparatus.

  At this time, for example, in order to reverse the transfer paper on which the toner image is formed on one side in order to discharge face-down (the image surface faces downward in order to align the transfer paper in the page order), the transfer paper is discharged. The paper is conveyed by the unit 218 to the double-sided paper conveyance path 220, is switched back by the reversing unit 221, and then is discharged to the paper discharge tray 219 through the reverse paper discharge conveyance path 222.

When images are formed on both sides of the transfer paper, the transfer paper on which the image is formed on one side is transported to the double-sided paper feed path 220 by the paper discharge unit 218 and switched back by the reverse unit 221. After that, it is sent to the duplex conveying unit 223.
The transfer paper sent to the double-sided conveyance unit 223 is fed again from the double-sided conveyance unit 223 in order to transfer the toner image formed on the photoconductor 215 again, and is again applied to the photoconductor 215 by the vertical conveyance unit 214. After the toner image is transferred to the other surface and transferred to the other surface, the toner image is fixed by the fixing unit 217 and discharged to the paper discharge tray 219 by the paper discharge unit 218.

  The photosensitive member 215, the conveyance belt 216, the fixing unit 217, the paper discharge unit 218, and the development unit 227 are driven by a main motor (not shown), and the driving force of the main motor is transmitted to each of the paper feeding units 211 to 213 by a paper feeding clutch. Driven. The vertical conveyance unit 214 is driven by the driving force of its main motor being transmitted via an intermediate clutch.

  The writing unit 250 includes a laser output unit 251, an imaging lens 252, and a mirror 253. Inside the laser output unit 251, a laser diode that is a laser light source and a rotating polygon mirror (polygon mirror) that scans the laser light. Or it has a vibrating mirror. Laser light emitted from the laser output unit 251 is deflected by a polygon mirror or a vibrating mirror, passes through an imaging lens 252, is folded by a mirror 253, and is focused on the surface of the photosensitive member 215.

  According to the image forming apparatus (digital copying machine) of the sixth embodiment, the image reading apparatus of the fifth embodiment is provided, and an image is formed on a recording medium based on image data read by the image reading apparatus. Further, it is possible to avoid a decrease in productivity (image formation throughput) such as a slow first copy time. In addition, it is possible to avoid concern about destruction of circuit components due to the occurrence of overvoltage. Therefore, it is possible to realize high quality of formed images, high speed image formation, and high processing efficiency.

  In the sixth embodiment, the present invention is applied to a digital copying machine. However, the present invention is not limited to this, and the present invention is not limited to an analog copying machine, but may be applied to other image forming apparatuses such as a digital multifunction machine and a facsimile machine. It can be applied. In the case of a digital image forming apparatus such as a digital copying machine, an image reading device including a light source driving device and an image forming unit that forms an image on a recording medium based on image data read by the image reading device. In the case of an analog image forming apparatus such as an analog copying machine, an image reading device is not provided, and an original (subject) is illuminated by irradiation light from a plurality of light sources by a light source driving device, Image forming means for forming an image by exposing a precharged image carrier with reflected light from the document is provided.

  As is apparent from the above description, according to the present invention, the light source driving device illuminates the subject with the irradiation light from the plurality of light sources, and receives the reflected light from the subject to perform processing. The boosting can be speeded up without generating an overvoltage with respect to the circuit components provided in each device. Therefore, it is possible to provide an image processing apparatus, an image reading apparatus, and an image forming apparatus that realize high image quality, high speed, and high efficiency by including the light source driving device.

10: First load 10a, 10b,..., 10n: LED light source array 20: Second load 30: Booster circuit 40, 90: LED driver 50: Connection switching circuit 60: OR gate 70: Cut-off circuit 80: RC circuit 100: Image reading apparatus 102: Light source 109: CCD 120, 300: ADF
151: Analog processing circuit unit 152: A / D conversion circuit unit 153: LVDS interface 200: Image forming apparatus 215: Photoconductor 217: Fixing unit 227: Development unit 250: Writing unit

JP 2008-187816 A

Claims (12)

A light source driving device for driving a plurality of light sources,
Boosting means for boosting a supply voltage from a power source and supplying the boosted voltage to the plurality of light sources;
Constant current driving means for constantly driving constant driving currents of the plurality of light sources to which the voltage boosted by the boosting means is applied;
Load means for consuming the same power as the plurality of light sources;
A light source comprising: a connection switching means for switching connection so as to selectively connect any one of the plurality of light sources and the load means between the boosting means and the constant current driving means. Drive device.   The connection switching means connects the load means to the boosting means from the start of boosting by the boosting means to completion of boosting, and connects the plurality of light sources to the boosting means after completion of boosting by the boosting means. The light source driving device according to claim 1, wherein the connection is switched so as to do.   The light source driving device according to claim 2, wherein the connection switching unit switches the connection in synchronization with a control signal from the outside. The light source driving device according to claim 2,
The constant current driving means is a means that is activated by an activation signal from the outside,
A light source driving apparatus comprising: a signal generation unit configured to generate a signal for causing the connection switching unit to perform connection switching based on the activation signal. In the light source drive device according to any one of claims 1 to 4,
A light source driving apparatus comprising: a blocking unit that electrically blocks the plurality of light sources so that the driving currents do not wrap around each other when the plurality of light sources are driven by the constant current driving unit.   The light source driving apparatus according to claim 5, wherein the blocking unit is a diode.   The light source driving apparatus according to claim 1, wherein the load unit is a resistor. In the light source drive device according to any one of claims 1 to 7,
A light source driving device comprising the light source driving device as a single integrated circuit.   9. A light source driving device according to claim 1, comprising: illuminating a subject with light emitted from the plurality of light sources by the light source driving device, receiving reflected light from the subject, and receiving an image signal. An image processing apparatus that performs image processing by converting the image into an image. The image processing apparatus according to claim 9 is an image reading apparatus,
An image reading apparatus that reads image data of the subject by the image processing.   11. An image forming apparatus comprising: the image reading apparatus according to claim 10; and image forming means for forming an image on a recording medium based on image data read by the image reading apparatus.   An image obtained by illuminating a subject with the light source driving device according to any one of claims 1 to 8 and light emitted from the plurality of light sources by the light source driving device and pre-charged with reflected light from the subject. An image forming apparatus comprising: an image forming unit configured to expose and image a carrier.

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